The present invention relates in general to a locking device for flexible, annular covers and in particular, to a lockup device for securing a cutting mat to a rotary anvil.
Rotary die cutting machines are used to cut a continuously moving workpiece by passing the workpiece through the nip of two generally cylindrical rotary components, a cutting roller and a rotary anvil. The cutting roller includes any combination of cutting blades or rules, and scoring elements projecting from the surface thereof. The rotary anvil provides a suitable surface to support the workpiece at the point where the work material is cut or scored by the cutting roller. Essentially, the rotary anvil serves as a backstop allowing the cutting blades to be urged against the work material to be cut or scored, without damaging the cutting blades themselves. Because of their speed of operation, rotary die cutting machines are used to perform cutting operations in numerous industries. For example, the corrugated industry utilizes such machines to cut and score corrugated paperboard materials for constructing packaging products such as boxes and shipping containers.
Typically, several cutting mats are axially aligned on a rotary anvil, such that a substantial portion of the rotary anvil is sleeved by the cutting mats. Each cutting mat is constructed of a deformable material such as a polymeric composition. The outer surface of the cutting mat is sufficiently rigid to give adequate support to the work material, yet soft enough so that the cutting blades will not wear or be damaged by impact with the rotary anvil. The rules or cutting blades on the cutting roller penetrate the cutting mats in operation. This leads to eventual fatigue and wear of the cutting mats, requiring periodic replacement.
At times, rotary die cutting machines are set up to feed a workpiece centrally, and as such, the full width of the rotary die cutting machine is not used. Under this circumstance, the cutting mats located generally in the central portion of the rotary anvil experience most of the wear. Likewise, the cutting mats located at the opposing end portions of the rotary anvil receive the least wear. To prolong the life of cutting mats, it is desirable to rotate the relative positions of the cutting mats on the rotary anvil, such that the cutting mats wear more evenly. Typically, a rotary anvil will hold between eight and fourteen cutting mats. Repositioning a number of cutting mats causes considerable downtime. The cutting mats wear continuously during cutting operations. As the cutting mats wear, the quality of the cutting operation deteriorates until the worn cutting mats are replaced. However, because of the considerable downtime in cutting mat rotation and changeover, the industry tendency is to prolong the time between cutting mat changeovers. This leads to a greater possibility of poor quality cuts.
Several techniques have been devised to secure the cutting mat to the rotary anvil. For example, several lockup devices comprise latching mechanisms built into flanged end portions of cutting mats. The flanged ends are interconnected and inserted into a channel of the rotary anvil itself, or in a slip bearing secured to the rotary anvil. In one device, a rotary anvil cover latching assembly includes a cutting mat having a female latch member, and an opposing flanged male latch member. The female latch member comprises a generally U-shaped metal frame having an upper segment, a side segment, and base segment. The rotary anvil includes a slip bearing having a channel extending longitudinally. A groove is provided along the intersection of each sidewall and the base of the channel, defining a pair of locking regions. The female latch member is inserted into the channel, such that the base segment rests on the base of the channel, and an angled end section of the base segment is received into one of the grooves. The mat is wrapped around the rotary anvil, and the flanged, male latch member is angled into the female latch member. However, cutting mats with this type of latch assembly have a tendency to pull away from the surface of the slip bearing and are difficult to mount because of the amount of compression required to force the male member into the final position within the female member. Difficulty in mounting such cutting mats leads to rotary die cutting machine downtime and infrequent cutting mat changeover.
Still other lockup devices comprise complimentary interlocking fingers cut into opposing ends of the cutting mat. Such devices attempt to eliminate the use of flanged end portions of a cutting mat and further eliminate the need for the channel in the rotary anvil. For example, one cutting mat construction comprises opposite ends having a plurality of complimentary fingers and receivers. The cutting mat is wrapped around the rotary anvil, and the ends are joined in puzzle like fashion. However, this construction may not provide suitable holding strength. Further, the ends of the cutting mat may pull away or slightly lift from engagement with each other causing one or more ridges or humps to be formed on the outer surface of the cutting mat. These ridges may interfere with the smooth operation of the rollers and as such, are detrimental to the rotary die cutting procedure. Cutting mats that incorporate interlocking fingers can also be difficult to install and mount leading to press downtime, and infrequent cutting mat changeover.
The present invention overcomes the disadvantages of previously known locking systems for cutting mats by providing a lockup device that allows for rapid cutting mat changeover, and installation. The lockup device comprises a base portion, one sidewall, and a wedge portion, and is inserted into a channel of a rotary anvil such that the sidewall of the lockup device is adjacent a wall of the channel. A cutting mat having opposing first and second flanged ends is wrapped around the rotary anvil. The first flange is compressed between the locking wedge and the sidewall of the lockup device. The second flange is compressed between the locking wedge and a channel wall. As such, the locking wedge and cutting mat are frictionally secured to the rotary anvil. Further, the cutting mat may be quickly repositioned by releasing the second flange from the channel. When the cutting mat is unwrapped from the rotary anvil, the lockup device remains secured to the first flange, allowing for quick repositioning.
In accordance with one embodiment of the present invention, a lockup device for securing a cutting mat to a rotary anvil is sized and dimensioned to fit within an axially extending channel along the surface of the rotary anvil. The lockup device comprises a base portion having first and second axially extending edges, and first and second transverse edges that correspond generally to the width of the axially extending channel. A sidewall projects from the first axial edge of the base. The height of the sidewall corresponds generally to the depth of the channel. The locking wedge further includes a locking wedge projecting from the base. The lockup device is insertable into the channel of the rotary anvil and is arranged to receive opposing first and second flanges of a cutting mat such that when the lockup device is inserted within the channel, and the opposing first and second flanges are received by the lockup device, the lockup device and the cutting mat are frictionally secured to the rotary anvil.
The locking wedge comprises a leg portion extending from the base. A pair of opposite, angularly outward extending locking surfaces project from the leg portion, and a pair of guide surfaces extend from their respective locking surfaces. The pair of guide surfaces are substantially inverted xe2x80x9cVxe2x80x9d shaped, each guide surface joining together at a common point. The locking surfaces frictionally hold the flanges of the cutting mat. As such, the locking surfaces may comprise any geometry that is disposed towards holding. For example, the locking surfaces may be arcuate, and comprise surface conditioning such as a knurled surface.
A first locking area is defined between the sidewall and the locking wedge, and a second locking area is defined between the locking wedge and the second axial edge of the base portion. When the lockup device is inserted within the channel, and a cutting mat is installed around the rotary anvil, the first flange of the cutting mat is frictionally held within the first locking area, and the second flange of the cutting mat is frictionally held within the second locking area. To improve the frictional fit of the first flange in the first locking area, the sidewall may comprise a non-uniform thickness, for example by tapering out as the sidewall extends out from the base portion. Further, the second flange is releasable from the second locking area such that when the cutting mat is unwrapped from the rotary anvil, the lockup device releases from the channel with the first flange remaining at least partially secured within the first locking area. This allows rapid replacement and moving of the cutting mats because only the second flange of the cutting mat need be released from the locking wedge in order to remove the cutting mat and the locking wedge from the channel.
The lockup device maintains the cutting mat securely fixed to the rotary anvil by frictional forces only. As such, there are no screws, bolts, or the like to slow down cutting mat changeover. The frictional forces are divided between the cutting mat and the lockup device so that relieving the frictional forces contributed by the cutting mat allows the lockup device to release easily from the channel. Specifically, when the lockup device is inserted within the channel, and the opposing first and second flange are received by the lockup device, the lockup device and the cutting mat are secured to the rotary anvil by frictional forces between the base portion and the channel floor, the side wall of the lockup device and the first channel wall, and the second flange and the second channel wall. By releasing the second flange from the second locking area, the friction retaining the cutting mat and the lockup device is partially relieved, allowing the lockup device to be easily removable from the channel.
In accordance with another embodiment of the present invention, a rotary anvil construction comprises a rotary anvil having a generally cylindrical surface and a channel axially disposed on the cylindrical surface, the channel comprising first and second channel walls projecting inward from the cylindrical surface. A lockup device is insertable into the channel and held therein by frictional forces only. The lockup device comprises a base portion having first and second axial edges, and first and second transverse edges. A sidewall projects from the first axial edge of the base, and a locking wedge projects from the base between the first and second axial edges.
The lockup device is insertable within the channel. A cutting mat has a first end terminating in a first flange, and a second end opposite the first end terminating in a second flange. The cutting mat is wrappable around the cylindrical surface of the rotary anvil such that the first flange is received in, and secured between, the locking wedge and the sidewall, and the second flange is received in, and secured between, the locking wedge and the second channel wall. As such, the lockup device and the cutting mat are frictionally secured to the rotary anvil. Further, upon removing the cutting mat from the rotary anvil by releasing the second flange from the channel and unwrapping the cutting mat, the lockup device releases from the channel, and the first flange remains at least partially secured between the locking wedge and the sidewall.
A plurality of lockup devices and corresponding cutting mats may be axially disposed within the channel, the plurality of lockup devices and cutting mats arranged such that any one of the cutting mats may be released from the rotary anvil without disturbing the remainder of the plurality of cutting mats.
According to yet another embodiment of the present invention, a lockup device for a rotary anvil comprises a base portion having first and second axial edges, and first and second transverse edges. A sidewall having non-uniform thickness projects from the first axial edge of the base, and a locking wedge projects from the base, and is positioned between the first and second axial edges, and spaced closer to the first axial edge than the second axial edge. A first locking area is defined between the sidewall and the locking wedge, and a second locking area is defined between the locking wedge and the second axial edge of the base.
The locking wedge has a cross section comprising a leg portion extending from the base, a pair of opposite, angularly outward extending arcuate, knurled locking surfaces projecting from the leg portion, and, a pair of guide surfaces substantially forming an inverted xe2x80x9cVxe2x80x9d shape, each guide surface extending from a respective one of the locking surfaces to join together at a common point.
The lockup device is arranged to fit into a channel of a rotary anvil. A first flange of a cutting mat is compressed into the first locking area, and a second flange of the cutting mat is compressed into the second locking area. As such, the lockup device secures the cutting mat to the rotary anvil by frictional forces only.
Accordingly, it is a feature of the present invention to provide a lockup device for securing a cutting mat to a rotary anvil, which is simple in construction and easy to use.
It is further a feature of the present invention to provide a lockup device that is insertable within a channel of a rotary anvil and that can secure a cutting mat to the cylinder portion of a rotary anvil using frictional forces only.
It is still another feature of the present invention to provide a lockup device that allows for quick cutting mat changeover and replacement without disturbing adjacent cutting mats.
Other feature of the present invention will be apparent in light of the description of the invention embodied herein.